Potassium channels in crustacean glial cells

Unitary currents through single ion channels in the glial cells, which ensheath the abdominal stretch receptor neurons of the crayfish, were characterized with respect to their basic kinetic properties. In cell-attached and excised patches two types of Ca(++)-independent K+ channels were observed with slope conductances of 57 pS and 96 pS in symmetrical K+ solution. The 57 pS K+ channel was weakly voltage-dependent with a slope of the Po vs. membrane potential relationship of +95 mV for an e-fold change in Po. In addition to the main conductance level, the channel displayed conductance levels of 80 and 109 pS. In excised patches, channel activity of this "subconductance" K+ channel showed "rundown" that could be prevented with 2 mM ATP-Mg on the cytoplasmic side of the membrane. The 96 pS K+ channel was strongly voltage-dependent with a slope of +12 mV for an e-fold change in Po. Averaged single-channel currents elicited by voltage jumps proved the channel to be of the delayed rectifying type. Channel activity persisted in excised patches with minimal salt solution and in virtually Ca(++)-free saline. Because of its dependence on intracellular ATP-Mg, the subconductance K+ channel is discussed as a target of modulation by transmitters or peptides via phosphorylation of the channel.